Okay, ignore the “burning for America part,” which is cheesy even by Bubba standards. What’s interesting here is that President Obama actually needed someone to go onstage and testify to his passion—to insist that, yes, it was in there somewhere. Most public figures are all outward passion, all backslapping, bear hugs, and (when the occasion calls for it) barely repressed tears.

“Cool on the outside” is something Americans rarely see in a politician; less charitable observers look at the same presidential quality and see “aloofness,” “standoffishness,” “arrogance,” and even the great American sin of not being “a people person.”

Sometimes it seems that we don’t know how to process a politician who wears emotions anywhere other than on his sleeve.

But Clinton’s line on Obama struck a familiar chord for us, because we’ve spent the past few years studying and writing on another politician famous for his coolness: Cato the Younger.

He was a practitioner of Stoicism, an ancient Greek religion that he helped bring to Rome. We aren’t claiming that the president’s a secret Stoic. But we do think that the public response to his self-control shows how poorly Stoic qualities can go over in our times: a philosophy built on emotional control seems strange in the age of over-sharing.

We think that’s a shame. Stoicism still has a tremendous amount to teach us, especially in these passion-saturated times. What’s more, the Stoic legacy has shaped our world in more ways than you might expect. Here are five reasons why Stoicism matters:

1. It was built for hard times.

Stoicism was born in a world falling apart. Invented in Athens just a few decades after Alexander the Great’s conquests and premature death upended the Greek world, Stoicism took off because it offered security and peace in a time of warfare and crisis. The Stoic creed didn’t promise material security or a peace in the afterlife; but it did promise an unshakable happiness in this life.

Stoicism tells us that no happiness can be secure if it’s rooted in changeable, destructible things. Our bank accounts can grow or shrink, our careers can prosper or falter, even our loved ones can be taken from us. There is only one place the world can’t touch: our inner selves, our choice at every moment to be brave, to be reasonable, to be good.

The world might take everything from us; Stoicism tells us that we all have a fortress on the inside. The Stoic philosopher Epictetus, who was born a slave and crippled at a young age, wrote: “Where is the good? In the will...If anyone is unhappy, let him remember that he is unhappy by reason of himself alone.”

While it’s natural to cry out at pain, the Stoic works to stay indifferent to everything that happens on the outside, to stay equally happy in times of triumph and disaster. It’s a demanding way of life, but the reward it offers is freedom from passion--freedom from the emotions that so often seem to control us, when we should control them. A real Stoic isn’t unfeeling. But he or she does have a mastery of emotions, because Stoicism recognizes that fear or greed or grief only enter our minds when we willingly let them in.

A teaching like that seems designed for a world on edge, whether it’s the chaotic world of ancient Greece, or a modern financial crisis. But then, Epictetus would say that--as long as we try to place our happiness in perishable things--our worlds are always on edge.

2. Stoicism is made for globalization.

The world that gave birth to Stoicism was a parochial, often xenophobic place: most people held fast to age-old divisions of nationality, religion, and status. If openly embracing those divisions sounds strange to us, we have Stoicism to thank. It was perhaps the first Western philosophy to preach universal brotherhood. Epictetus said that each of us is a citizen of our own land, but “also a member of the great city of gods and men.” The Roman emperor Marcus Aurelius, history’s best-known Stoic, reminded himself daily to love the world as much as he loved his native city.

If the key to happiness is really in our own wills, then even the biggest social divides start to look trivial. The Roman Stoic Seneca lived in a society built on slavery, but he also urged his fellow Romans to “remember that he whom you call your slave sprang from the same stock, is smiled upon by the same skies, and on equal terms with yourself breathes, lives, and dies.”

This embrace of cosmopolitanism (a word invented by Stoics, which literally means world-city) made Stoicism the ideal philosophy for the Roman Empire, which brought an unprecedented range of races and religions into contact. Stoicism made sense for a globalized world--and it still does.

3. If you’re Christian, you’re already part-Stoic.

Imagine a religion that stressed human brotherhood under a benevolent creator God; that told us to moderate and master our basic urges rather than giving into them; that nevertheless insisted that all humans, because we’re human, are bound to fail at this mission; and that spent a lot of time talking about “conscience” and the multiple aspects, or “persons,” of a unitary God. All of that might sound familiar. But the philosophy that invented all of those ideas was not Christianity, but Stoicism.

It makes sense that Christianity is a deeply Stoic religion. Stoicism dominated Roman culture for centuries—and Christianity went mainstream in the same culture. What’s more, many of the leaders of the early Christian church were former Stoics. Of course Christianity borrowed much of its thought and terminology from Stoicism--because thinking about religion in the early 1st millennium meant thinking like a Stoic.

As Christianity continued to grow, church leaders, who wanted to emphasize the uniqueness of their faith, began to downplay this Stoic connection. But Stoicism is still there at the foundation of the Christian religion, in some of its most basic terms and concepts.

4. It’s the unofficial philosophy of the military.

In 1965, James Stockdale’s A-4E Skyhawk was shot down over Vietnam. He later remembered the moment like this: “After ejection I had about thirty seconds to make my last statement in freedom before I landed...And so help me, I whispered to myself: ‘Five years down there, at least. I’m leaving the world of technology and entering the world of Epictetus.’”

Stockdale spent more than seven years in a Vietnamese prison, and he wrote that Stoicism saved his life. Stockdale had spent years studying Stoic thought before deploying, and he drew on those teachings to endure his captivity. These words from Epictetus kept coming back to him: “Do you not know that life is a soldier’s service?...If you neglect your responsibilities when some severe order is laid upon you, do you not understand to what a pitiful state you bring the army?” While some of his fellow POWs tormented themselves with false hopes of an early release, Stockdale’s Stoic practice helped him confront the grim reality of his situation, without giving in to despair and depression.

Stockdale was not alone as a military man who drew strength from Stoicism. In her book The Stoic Warrior, Nancy Sherman, who taught philosophy at the Naval Academy, argued that Stoicism is a driving force behind the military mindset--especially in its emphasis on endurance, self-control, and inner strength. As Sherman writes, whenever her philosophy class at Annapolis turned to the Stoic thinkers, “many officers and students alike felt they had come home.”

5. It’s a philosophy for leadership.

Stoicism teaches us that, before we try to control events, we have to control ourselves first. Our attempts to exert influence on the world are subject to chance, disappointment, and failure--but control of the self is the only kind that can succeed 100% of the time. From emperor Marcus Aurelius on, leaders have found that a Stoic attitude earns them respect in the face of failure, and guards against arrogance in the face of success.